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| 型號(hào)： | DS1238A |
| 英文描述： | CAP 3.0UF 250VAC METALLIZED POLY |
| 中文描述： | 微管理器芯片 |
| 文件頁(yè)數(shù)： | 4/13頁(yè) |
| 文件大?。?/td> | 211K |
| 代理商： | DS1238A |
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DS1238A
4 of 13
full period as outlined in NO TAG. The
WDS
pin will remain low until one of three operations occurs.
The first is to strobe the
ST
pin with a falling edge, which will both set the
WDS
as well as the watchdog
timer count. The second is to leave the
ST
pin open, which disables the watchdog. Lastly, the
WDS
pin is
active low whenever V
CC
falls below V
CCTP
and activates the
RVT
signal. The
ST
input can be derived
from microprocessor address, data, or control signals, as well as microcontroller port pins. Under normal
operating conditions, these signals would routinely reset the watchdog timer prior to timeout. The
watchdog is disabled by leaving the
ST
input open, or as soon as V
CC
falls to V
CCTP
.
NON-MASKABLE INTERRUPT
The DS1238A generates a non-maskable interrupt (
NMI
) for early warning of a power failure to the
microprocessor. A precision comparator monitors the voltage level at the IN pin relative to an on-chip
reference generated by an internal band gap. The IN pin is a high-impedance input allowing for a user-
defined sense point. An external resistor voltage divider network (NO TAG) is used to interface with high
voltage signals. This sense point may be derived from the regulated 5-volt supply, or from a higher DC
voltage level closer to the main system power input. Since the IN trip point V
TP
is 1.27 volts, the proper
values for R1 and R2 can be determined by the equation as shown in NO TAG. Proper operation of the
DS1238A requires that the voltage at the IN pin be limited to V
IH
. Therefore, the maximum allowable
voltage at the supply being monitored (V
MAX
) can also be derived as shown in NO TAG. A simple
approach to solving this equation is to select a value for R2 of high enough value to keep power
consumption low, and solve for R1. The flexibility of the IN input pin allows for detection of power loss
at the earliest point in a power supply system, maximizing the amount of time for microprocessor
shutdown between
NMI
and RST or
RST
.
When the supply being monitored decays to the voltage sense point, the DS1238A will force the
NMI
output to an active state. Noise is removed from the
NMI
power-fail detection circuitry using built-in
time domain hysteresis. That is, the monitored supply is sampled periodically at a rate determined by an
internal ring oscillator running at approximately 30 kHz (33
μ
s/cycle). Three consecutive samplings of
out-of-tolerance supply (below V
SENSE
) must occur at the IN pin to active
NMI
. Therefore, the supply
must be below the voltage sense point for approximately 100
μ
s or the comparator will reset. In this way,
power supply noise is removed from the monitoring function preventing false trips. During a power-up,
any IN pin levels below V
TP
detected by the comparator are disabled from reaching the
NMI
pin until
V
CC
rises to V
CCTP
. As a result, any potential active
NMI
will not be initiated until V
CC
reaches V
CCTP
.
Removal of an active low level on the
NMI
pin is controlled by the subsequent rise of the IN pin above
V
TP
. The initiation and removal of the
NMI
signal during power up depends on the relative voltage
relationship between V
CC
and the IN pin voltage. Note that a fast-slewing power supply may cause the
NMI
to be virtually nonexistent on power-up. This is of no consequence, however, since an RST will be
active. The
NMI
voltage will follow V
CC
down until V
CC
decays to V
BAT
. Once V
CC
decays to V
BAT
, the
NMI
pin will enter a tri-state mode.
ST INPUT TIMING
Figure 2
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| DS1238A-10 | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)電壓: 欠電壓閾值: 過(guò)電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開(kāi)關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| DS1238A-10+ | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)電壓: 欠電壓閾值: 過(guò)電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開(kāi)關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| DS1238A10N | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog IC |
| DS1238A-10N | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)電壓: 欠電壓閾值: 過(guò)電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開(kāi)關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| DS1238A-10N+ | 功能描述:監(jiān)控電路 RoHS:否 制造商:STMicroelectronics 監(jiān)測(cè)電壓數(shù): 監(jiān)測(cè)電壓: 欠電壓閾值: 過(guò)電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開(kāi)關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
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